Abstract: Set single capacitance sensor in magnetic liquid level meter as research object, and respectively use infinite elements and hybrid finite element—Trefftz method to make mathematic model about electrostatic field. Based on the model, use ANSYS software to analyze the change of electric field arosed by magnetic pole turning around and count the change rate of capacitance in the working process of the level meter. After compared with the experiment results, the relative error of simulated value using Trefftz method is 3.3% and then Trefftz method is proved to be a proper way to solve the electrostatic problems with open boundary.

Key words: Boundary element method, Capacitance, Finite element method, Mathematic model, Trefftz method